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tomka avatar image
tomka asked

Low solar wattage in full sun

Hi guys,


Have been trying to figure this one out by myself and by reading other posts but I’m not getting anywhere. Hopefully somebody here can help.

I live in a van and have the following setup:


160w Blackline solar panel

2x 12V DC 75Ah Batteries in parallel

Victron MPPT 75/15 (no Bluetooth for app)

Victron Multiplus Compact 12/800/35-16

Victron Battery Display


We spent the last two months in very warm weather. Most of the days in full sun.

Yet I haven’t seen the wattage go above 90 watts. I’m sure it’s not in float since it even stays fairly low around 70%.

Yesterday I left the van in the morning around 09.00 and came back at 17.00 with all appliances turned off. It was in full sun all day and yet it only charged from 63% to 78%.

The previous owner tells me that, on a sunny day, it should do around 150 watts and that he got to 125 watts in February. I’m now in Italy in summer and I am not seeing those numbers. Recently it’s even been not much more than 50.


The whole thing has quite an impact on the way we live because we end up driving a lot more simply to charge our batteries.


Hope somebody has an idea.


Thanks!

Solar Panel
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spirou avatar image spirou commented ·

Forget the % display for a moment. I'd argue its nearly useless for those that don't spend a considerable effort calibrating parameters. Give us a screenshot from the VRM app of the daily charge profile (min/max batt voltage, charge phase duration etc.)
Also, is it a flex or solid panel and how is it mounted?

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tomka avatar image tomka spirou commented ·

Unfortunately I don’t have the ‘smart’ device nor a Bluetooth dongle. So cant get the info on the app. The panel is solid and mounted on the top. It was put there by the owner before the previous owner so I also have very limited info about the panel. This makes it a bit trickier to figure out what the expected output should be. However, the previous owner said that max 90 is odd in sunny conditions.

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Jesse avatar image Jesse tomka commented ·

Bluetooth dongles for your MPPT are relatively cheap and addictively informative, many hours can be lost watching the numbers...

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spirou avatar image spirou tomka commented ·

Nevermind the app then. What is the battery voltage early in the morning before the sun is high enough to start charging and does it ever reach absorption voltage then float?

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tomka avatar image tomka spirou commented ·

I’ll check that again tomorrow morning. In history it shows that highest voltage was 15V. For absorption the orange LED should be blinking slowly but haven’t seen that occur in the last couple of days. It’s only blinking fast.

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tomka avatar image tomka spirou commented ·

Battery voltage early morning is 12V

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rickp avatar image rickp commented ·

I recently saw a van-lifer in Italy who had a rail partially shading his panel. Any shading, even a very small bit, will knock a single panel’s production to a fraction of its potential. Make sure nothing on the roof is casting a shadow: wires, racks, luggage, fan covers, etc. Check wiring and connections, as well. Poor or damaged connections waste energy as heat, and can be a fire danger if left unaddressed.


Next you can check the panel voltage to see if it is operating correctly, aside from other components. There are many videos out to show you how. Then test one step further at a time. Ultimately, the batteries may be at a diminished capacity and are charging as high as they will. A step-by-step approach is best to troubleshoot these things. Viewing it as a system can introduce confusing variables.

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tomka avatar image tomka rickp commented ·

Thanks for this. The panel is fully exposed to the sun but I’ll check everything thoroughly on top tomorrow again. Not sure about the voltage at this point because I don’t have the exact details of the panel. Gettin the idea that it’s an older version of the ones they’re currently selling.

It has been very warm the last couple of weeks and especially inside the van has felt like a sauna at times. Is it possible that this has caused damage to the cables or batteries?

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Jesse avatar image Jesse tomka commented ·

Lots of lower quality or older panels will drop their output dramatically when too hot. I have a 200W panel which never goes above 120W in summer but routinely reaches 200W in cool weather.

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marekp avatar image marekp Jesse commented ·

That is correct.

Older panels usually have power temp. coefficient around -0.4-0.5 % per deg. (with full power at 25C).

To loose over 60% of power, temperature of the panel would be over 140 deg Celsius. I suppose it could be possible since I have seen someone fry eggs on the pavement. :)

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marekp avatar image
marekp answered ·

When did you last time clean this panel?

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tomka avatar image tomka commented ·

That I did multiple times to make sure that wasn’t the problem :)

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